Injection of additives into molten metal baths is often accomplished by encasing the additives in a metal jacket or sheath to form a “cored wire,” and then adding the cored wire to the molten metal bath, where the metal jacket or the sheath component of the wire melts and releases the additives. For example, an additive that may be added to steel is calcium. The calcium may be provided in the form of a wire that is insulated with paper and an additional jacket/sheath of steel.
To add a cored wire to a metal bath, a feeder (often referred to as an “injector”) is used. The feeder pulls cored wire from a reel or cage, straightens the wire and pushes the straightened wire through a metal guide tube. A guide tube is generally a steel tube having a diameter between 25 millimeters and 150 millimeters, depending on equipment conditions. Often, recovery is best when the guide tube diameter is on the lower end of the range, for example, between 25 millimeters and 50 millimeters. The metal guide tube directs the cored wire on a trajectory so that the cored wire enters the molten metal bath to facilitate dissolving the cored wire in the molten metal.
For example, calcium is very reactive, has a low density relative to molten steel and forms a vapor at molten steel temperatures if it dissolves near the surface of the molten steel. To direct the wire deep into the metal bath, and thereby guard against dissolving near the surface of the molten steel bath, a guide tube may be used that is able to be positioned near the molten steel and survive the splashing of molten steel and slag while the calcium-cored wire is added to the molten steel. Usually, the cored wire is added to the molten steel for three to four minutes.
It has been shown that when the guide tube is placed close to the surface of the molten metal, more of the additive ends up in the molten metal. The “recovery” is the amount of additive measured in the molten metal divided by the amount of additive injected into the molten metal. Several factors determine the recovery of the additive. In almost all cases, greater recovery is desired. Factors which influence the recovery include the cored wire's angle of entry into the metal bath, the velocity at which the cored wire enters the metal bath, and the distance between the tip of the guide tube and the surface of the metal bath.
Recovery is usually improved if an end of the guide tube is placed close to the metal bath. However, experience shows that the end of the guide tube will be removed either by melting or oxidizing the guide tube, or the guide tube will become plugged if the guide tube is brought too close to the metal bath. Melting, oxidation and/or plugging have been observed when the distance between the guide tube and the metal bath is less than one meter. To avoid these conditions, a large, dense ceramic end-piece may be used on the end nearest the molten metal. However, such an end-piece is susceptible to metal and slag build-up on the ceramic end. Further, the weight of the end-piece makes handling difficult. In addition, build-up ultimately blocks the guide tube if the tube is lowered near the metal bath.
Consequently, there is a need for a new device that is able to withstand the temperatures and splashing of slag and metal, while reducing buildup, and at the same time is able to withstand mechanical abrasion and impact energy from the wire that is being added to the molten metal bath.